I understand what bump stocks do from reading up on them, but I haven’t found an explanation of how they work. They allow firing a semi-automatic weapon more quickly by using recoil to move the rifle back and forth (“bumping”) against the trigger finger. What I don’t understand is what is different in a bump stock compared to a regular stock. In my mind, I envision a big cartoonish spring in the bump stock that moves the rifle back forward after the initial kick from recoil. How does it work exactly?
In: Physics
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So bump firing is a technique to get a semiautomatic firearm to fire repeatedly. It works because the receiver, stock, grips, and your arms/shoulder all act as a spring-mass-damper system together. When you fire the weapon, it recoils back into your grip, and then shifts forward again as your grip/shoulder pushes the gun back forwards. If you adjust your stance a bit, or use stiffer objects than your finger over the trigger (e.g. a stick), you can ensure that each time the weapon cycles and begins to shift forwards, the trigger will get pulled again and keep firing as fast as the weapon can cycle.
You can hypothetically do it with any semi-automatic weapon, with no modifications, but realistically it’s only ever something you can do on rifles, and it’s typically a sign that the trigger mechanism was installed poorly or is going bad. It’s also something that can be done deliberately with no real effort (e.g. using the belt loop on your jeans to stiffen your trigger finger, using a stick off the ground, etc.).
You can also modify the weapon to make bump firing more easily achievable, typically by just adjusting the trigger mechanism or by modifying the stock to change how stiff it is. However, you can take it a step further and use a bump stock.
A stereotypical bump stock also allows the receiver to move back and forth into the stock (against a spring), which also makes bump firing easier.
“True” bump stocks could hypothetically be regulated because they tend to all work the same way, kinda, and because they essentially have no purpose other than making bump firing easier (because the bump stock is a really really shitty stock, by design), but bump firing itself would be impossible to regulate.
Inertial impact of the cycling bolt (recoil) has enough motion on the overall firearm to allow for a trigger reset, and with muscle memory the trigger finger can be placed at the breakpoint of the trigger for a fire rate close to or at the cycle rate of the firearm.
It does not increase the cycle rate of the firearm (that is static and based on the bolt weight / buffer system). It does make it easier for a person to shoot faster than they normally could. But anyone proficient with their firearm can do the same with or without a bumpstock.
Rather than ‘pulling’ the trigger, you basically point your trigger finger in a fixed position and push the gun into your finger.
The stock slides, and has play. No springs. You push forwards with your non-trigger hand, and pull backwards with your trigger hand. Recoil pushes the rifle backwards (deeper into the stock). This allows the trigger to reset and be ready to fire again. At which point the forward pressure from your non trigger hand reasserts and moves the gun forwards, pushing the trigger into your waiting trigger finger, firing the gun and setting off the cycle again.
Here’s a video showing one in operation, highlighting the sliding action. Notice the trigger and grip move relative to each other.
basically two things: first lets you press your trigger finger against a ledge to make it easier to keep in place while letting the gun move back into the stock with recoil, such that the trigger moves back and forth into your trigger finger from recoil
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A bump stock lets the gun float a little bit, so when it fires, the whole gun moves backward a little bit before hitting your shoulder. A spring then pushes the whole gun forward again, and (assuming you haven’t moved your trigger hand) pushes the trigger against your finger, which causes it to fire again. This cycle repeats.
It’s just a spring inserted between the butt of the gun and your shoulder along with some plastic to make it more comfortable to hold. Instead of moving your finger back and forth to pull the trigger, you’re moving the whole gun back and forth and keeping your finger in the same place.
Think about bouncing a basketball.
A manual rifle (e.g., bolt action) is like a ball that doesn’t bounce. You have to pick the ball up to drop it again.
A semi-automatic rifle is like a ball that bounces back up to your hand. You still need to push down again to keep the dribble going, but the ball has essentially reset itself.
A bump stock is like a basketball with extra bounce. So now, you just need to keep your hand in the same place and the ball will keep dribbling.
A bump stock does this by taking the energy of the rifle’s kickback and using it to move the trigger away from your finger and then shoving the trigger back into your finger.
The stock is able to float back and forth about an inch. You start with it fully extended.
You pull the trigger, the gun fires and recoils back into the stock.
As the gun goes backwards, a protrusion from the stock pushes your finger off the trigger so that it can reset.
You pull the rifle forward with your support hand and doing so it pulls the trigger into your finger and it fires again.
By simultaneously pulling backwards with your trigger finger and pushing forwards with your support hand, the system forces your finger to keep on firing and releasing the trigger pretty quickly.
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